This dissertation concerns the acquisition of mappings between lexical meaning and syntactic form in which arguments in the surface syntactic form may be left implicit, specifically focusing on indefinite implicit objects in English, e.g., John is eating (something).

First, in an analysis of the adult grammar, gradient grammaticality of an indefinite implicit object across verbs is derived from two factors—higher semantic selectivity of the verb and the aspectual properties of atelicity and imperfectivity. Using an Optimality Theory framework (Prince and Smolensky, 1993/2004), a probabilistic ranking of constraints is proposed. Acquisition of the mature grammar is argued to require well-developed knowledge about verbs' argument structures and selectional preferences. The learner must note the range of arguments from which a verb selects its objects and coordinate this information with the possible occurrence of the verb in the implicit object construction.

Second, young children's knowledge of verbs' selectional preferences is assessed by looking at the range of objects used across verbs in spontaneous speech and in an elicited production task (2;6–3;0 and 3;6–4;0 yrs). For both age periods, children's usage of objects is found to be slightly semantically broader than their mothers' usage, but importantly the verbs that are increasingly more selective in the mothers' usage are also shown to be of higher selectivity in the children's usage, thus putting children in a position to recognize the systematicity with which implicit objects are used in the input.

Third, the spontaneous speech of a young child and her mother (same age periods as above) are examined. Although the child omits more objects than her mother during the younger age period, during both age periods her use of indefinite implicit objects (but not definite implicit objects) is shown to accord with higher semantic selectivity and atelicity, as does her mother's. She differs from her mother mainly by using low rates of indefinite implicit objects with verbs of low semantic selectivity and/or telic verbs. These results show that by the time the child has learned verbs' selectional preferences that she can largely successfully restrict her use of implicit objects accordingly.